1. Field of the Invention
This invention relates to the utilization of geothermal energy, and more particularly to a process for deriving useful energy from geothermal brines.
2. Description of the Prior Art
As conventional hydrocarbon fuel resources have become less abundant and more expensive, a worldwide emphasis has been placed on the development of alternative energy resources, such as geothermal energy resources. Electricity and other forms of useful energy can be derived from geothermal resources by producing geothermal steam and/or aqueous geothermal liquids from a subterranean geothermal reservoir and processing the produced geothermal fluid in surface facilities to extract thermal energy therefrom. Of particular interest is the generation of electricity by passing geothermal steam, such as geothermal steam flashed from a hot geothermal brine, through a steam turbine/generator.
Most hot aqueous geothermal fluids are produced from subterranean geothermal reservoirs as a two-phase fluid comprising a vapor phase containing steam and non-condensible gases, such as hydrogen sulfide, and a hot liquid phase or "brine" containing heavy and/or transition metals, silica and other scale-forming species. Apart from the precipitation, scaling and corrosion problems associated with the hydrogen sulfide content of these two-phase fluids (as discussed in U.S. Pat. No. 4,244,190), other scale-forming species, such as iron, calcite and silica, pose severe problems which must be overcome to achieve the successful derivation of useful energy therefrom. The scale-forming tendencies of these geothermal brines vary widely, roughly in proportion to their salt content, from brines having little or no tendency to deposit amorphous silica, calcite or the like to brines having severe scaling tendencies. In the handling of geothermal brines having a severe tendency to deposit amorphous silica or calcite upon a reduction in its pressure or temperature, it has been particularly difficult to flash motive steam from such a brine without undesirably causing so much deposition of amorphous silica and/or calcite in and/or upstream of the flash vessel that continuous derivation of useful energy from such brines has been extremely difficult at best. Thus, a need exists for a practical process for deriving useful energy from such brines.
Accordingly, it is a primary object of this invention to provide a practical process for the derivation of useful energy from geothermal brines having relatively severe tendencies to deposit amorphous silica or calcite upon a reduction in the temperature or pressure of the brine.
It is another object of this invention to provide a process in which the deposition of amorphous silica and/or calcite from a hot geothermal brine is substantially inhibited during the flashing of steam from the brine.
Further objects, advantages and features of the invention will become apparent to those skilled in the art from the following description when taken in conjunction with the accompanying drawing.